Subculture-induced protein synthesis in tissue cultures of Glycine max and Phaseolus vulgaris

Alcohol dehydrogenase (EC 1.1.1.1) isozymes as markers at 2,4-dichlorophenoxyacetic acid x kinetin combinations in callus cultures of Cereus peruvianus (Cactaceae)

Alcohol dehydrogenase (ADH; EC 1.1.1.1) isozymes were investigated in tissue of Cereus peruvianus cultured in different concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D) and kinetin. Five ADH isozymes were detected in starch gel and showed different patterns in seeds, seedlings, calli cultured at 32 and 22 degrees C, and plants regenerated from calli cultured in three 2,4-D and kinetin combinations. Four phenotypes formed by different combinations of ADH-2, ADH-3, ADH-4, and ADH-5 were detected in calli cultured at 32 degrees C and in plants regenerated from calli. ADH-1 isozyme was detected only in calli subcultured for 1 or 2 weeks at 22 degrees C and was indicated as a marker of stress conditions that affect the growth of C. peruvianus callus tissues in culture. ADH phenotypes with either a higher or a lower number of isozymes were detected in different proportions in the callus tissues cultured in media containing different 2,4-D and kinetin ratios. ADH isozyme patterns were found to be sensitive markers at the highest kinetin concentration or at high kinetin/2,4-D ratios. The results indicate a high correlation between the ADH isozyme patterns and the capacity for regeneration. Thus, ADH isozymes are indicated as good biochemical markers and as a powerful tool for monitoring studies of C. peruvianus callus cultures.

Use of antisera to localize callose, xylan and arabinogalactan in the cell-plate, primary and secondary walls of plant cells

Antibodies to cellobiose, L-arabinopyranose, L-arabinofuranose, D-galactose, oligosaccharides containing β1→4 xylose, oligosaccharides containing β1→4 glucose, and oligosaccharides containing β1→3 glucose have been raised in rabbits. The antisera have been characterized to show the specificity of binding to particular polysaccharides. They have been used for immunocytology using the electron microscope to locate the polymers in dividing and differentiating cells of bean (Phaseolus vulgaris L.) root, bean callus tissue and cells of Zinnia elegans L. in vitro. Arabinogalactans have been shown to be present in the cell-plate and primary walls but not in secondary thickening. Xylan as distinct from xyloglucan was found in the primary walls but not in the cell-plate. It was present in large amounts in the secondary thickening. Callose was found in the cell plate and also in the young growing wall. In the wall it was specifically located at the plasmodesmata. The use of the antibody against L-arabinofuranose enabled a specific organelle to be detected which was membranous and which occurred within the cytoplasm and also within the vacuole of the cells. Membranes carrying polymers containing L-arabinofuranose were also found in layers just under the plasmamembrane.

Kinetin-induced stimulation of electrogenic pumping in soybean suspension cultures is unrelated to signal transduction

Primary modes of action of cytokinins have been thought to involve stimulation of the electrogenic H(+) pump and-or opening of plasmamembrane Ca(2+) channels. In order to test these hypotheses, rapid changes in membrane transport in response to cytokinin application were studied in heterotrophic suspension-cultured callus of soybean (Glycine max (L.) Merr.) using electrophysiological techniques. Kinetin (N(6)-furfurylaminopurine; 2 μM) elicited membrane hyperpolarization of 13±1 mV. This effect occurred even at membrane poteintials more negative than the most negative ionic equilibrium potential, and therefore might have resulted either from stimulation of the electrogenic pump, or from closure of ionic channels. The former mechanism of action appears most likely because (i) kinetin-induced membrane hyperpolarization is not accompanied by a significant change in plasma-membrane resistivity and (ii) hyperpolarization is abolished by cyanide, which inhibits electrogenic pump activity by depletion of cellular ATP.Electrogenic pumping is also activated by two other cytokinins: N(6)-(benzyl)adenine and trans-zeatin. However, it is unlikely that the hormonal effect on electrogenesis is directly related to transduction of the cytokinin signal, for the following reasons: (i) hormonally inactive, but chemically related compounds (cis-zeatin, adenine) also elicited membrane hyperpolarization; (ii) hormonally active, N(9)-substituted cytokinins failed to stimulate electrogenesis; (iii) the chemically unrelated cytokinin N,N'-diphenylurea also failed to stimulate electrogenesis.The results imply that the kinetin effect on electrogenic pumping is related to adenine, or its metabolism, and not hormonal action. Adenine was absorbed by soybean cells, but not in sufficient quantities to have a significant effect on adeninenucleotide pools. It appears likely that the control of electrogenesis requires either the presence of a purine free base (i.e. no substituents at the N(9) position) or phosphoribosylation of the free base. No evidence was found for cytokinin-induced Ca(2+)-channel opening, though it is argued that such an event might be physiologically relevant, yet undetectable with the methods employed. It is essential that future studies on cytokinin signal transduction - especially as they relate to membrane transport - take into account the possibility that metabolic effects unrelated to hormone action are dominant.

Purification, immunoassay and characterization of an abundant, cytokinin-regulated polypeptide in cultured tobacco tissues : Evidence the protein is a β-1,3-glucanase

We have purified an abundant, 33000-dalton polypeptide (P33) from cultured pith parenchyma tissue of Nicotiana tabacum L. cv. Havana 425. The accumulation of P33 in culture is inhibited by the cytokinin kinetin (N(6)-furfuryl-amino purine). When tissues are subcultured on auxin-containing medium, the P33 content measured by rocket immunoelectrophoresis increases by 10-fold from 9 to 90 μg·mg(-1) soluble protein over a 7-d period. This increase is blocked when kinetin is added to the culture medium. There is strong evidence that P33 is a β-1,3-glucanase (EC 3.2.1.39): i) Purified P33 specificially promotes the endo-type hydrolysis of β-1,3-glucans and has essentially the same moleculear weight, pH optimum, and sensitivitiy to heavy metals as the β-1,3-glucanase isolated by others from tobacco. ii) Glucanase activity is inhibited by specific antibodies against P33. iii) P33 and glucanase activity co-purify and cannot be separated by affinity chromatography using the β-1,3-glucanase substrate pachyman. iv) P33 content and glucanase activity are strongly correlated in tissues grown under inductive and non-inductive conditions. The pattern of glucanase synthesis estimated by [(35)S]methionine incorporation parallels changes in the amount of glucanase. This indicates that cytokinin acts, at least in part, by blocking synthesis of the enzyme.

Immunological estimation of changes in the absolute amounts of nuclear RNA polymerases in strictly auxin-requiring, cultured soybean cells upon addition of 2,4-dichlorophenoxyacetic acid

Soybean cells were subcultured in the presence of 4 μM 2,4-dichlorophenoxyacetic acid (2,4-D;=stock cells), or transferred and subcultured in a culture medium depleted of 2,4-D (=control cells), then reincubated with 4 μM 2,4-D (=treated cells). Control cells responded to 2,4-D by resuming cell division and DNA, RNA and protein synthesis at levels which were comparable to those of stock cells. This study system was used to investigate auxin effects on RNA polymerases. Both activities of RNA polymerases and their absolute amounts in extracts from stock, control and treated cells were determined, using the in-vitro assy of transcription of denatured calf thymus DNA and the specific quantitative immunological method reported in Miassod and Got (1984, Planta 162, 427-434), respectively. The data showed that the levels of enzymes did not remain constant in the stock cells during the subculture cycle, that auxin treatment enhanced, by a factor of two to four, the amounts of RNA polymerase I and II, expressed as percents of total proteins of soybean cells, and that this increase was not necessarily reflected by a parallel increase of the activity measured in the in-vitro test.

Molecular cloning and characterisation of cDNAs complementary to mRNAs from wounded potato (Solanum tuberosum) tuber tissue

Five cDNA clones complementary to mRNAs representing different abundances and responses to wounding have been isolated from a library of Sau 3A fragments in the bacteriophage M13 mp8. These were characterised by hybrid-release translation and hybridisation to RNA blots. The levels of RNA complementary to two of the clones show a marked increase during the 24h after wounding, one shows a small increase and two show no appreciable changes except that caused by a general increase in the total amount of polyadenylated RNA per microgram of total RNA which increases 2.5-fold during the same period. The would-induced RNAs are not induced in diluted suspension-culture cells, but RNA complementary to each clone is present in varying levels in stems, leaves and roots of intact potato plants.

Changes in levels of transcripts in endosperms of castor beans treated with exogenous gibberellic acid

A complementary-DNA library to mRNA from castor-bean endosperm has been prepared. Three clones have been examined in detail. One of these is complementary to isocitrate-lyase mRNA. The other two clones code for proteins with M r , 42000 and 38000. All three clones have been used to measure levels of transcripts during seed germination. The three transcripts all increased during germination and the rate of their appearance is stimulated by exogenous GA3. The data strongly support the view that the action of GA3 in these seeds is to stimulate non-specifically the rate of transcription and, in turn, protein synthesis. Possible mechanisms for the action of the growth regulator are discussed.

Evidence for an abundant 33,000-dalton polypeptide regulated by cytokinins in cultured tobacco tissues

When cloned pith and leaf tissues of Nicotiana tabacum L. cv. Havana 425 are subcultured for 3 d on auxin-containing medium and labelled for 18 h with [(35)S]methionine, up to 10% of the labelled, soluble-protein fraction is found in a single band with an apparent molecular weight of approx. 32,000-34,000 dalton on sodium-dodecylsulfate polyacrylamide-gel electrophoretograms. The labelling of this band, designated P33, is dramatically inhibited by the cytokinin, kinetin, in some cell lines at concentrations as low as 1.4·10(-8) M. P33 is a major component of the protein fraction obtained from non-habituated clones, cytokinin-habituated clones, and revertant subclones of crown-gall-transformed clones, but cannot be detected in clones habituated for both auxin and cytokinin, or crown-gall-transformed clones. The evidence supports the hypothesis that cytokinin in the presence of auxin regulates the production of a specific, major polypeptide in the soluble-protein fraction of the tissue and that this protein is not produced in tissues autotrophic for both auxin and cytokinin.

The action of exogenous gibberellic acid on polysome formation and translation of mRNA in germinating castor-bean seeds

The amount of protein synthesis in germinating castor-bean seeds has been estimated by the quantitative and qualitative exmainatin of polysomes from the seeds in the presence and absence of gibberellic acid (GA3). Careful optimisation of polysome extraction procedures was required to minimise the ribonuclease activity in the extracts. Ribonuclease activity in seed extracts increased fourfold over the first 5 d of germination. Gibberellic acid stimulated polysome formation about twofold during the first 4 d of germination. It also stimulated the amount of mRNA associated with polysomes by about twofold during the first 3 d of germination. Between days 1 and 5 of germination, polysome formation was primarily limited by mRNA availability. During the period 0-24 h, polysome formation was independent of mRNA levles. The increase in enzyme activities stimulated by GA3 was probably the result of an increase in the amount of cellular mRNA. No evidence was obtained for an action of GA3 on translation other than on the increased production of RNA. Examination of the recruitment of isocitrate-lyase mRNA into polysomes showed that GA3 did not specifically stimulate production of this enzyme.

Some rapid effects of synthetic auxins on mRNA levels in cultured plant cells

When bean and soybean tissue culture cells were subcultured into fresh medium the translatable levels of a small group of mRNAs increased rapidly and then decreased to a low level 10 h after subculture. By starving the cells of auxin and then subculturing them into media with or without auxin, it was found that the increase in translatable mRNA for certain proteins was strongly dependent on auxins. The rapidity of this effect suggested that auxins can directly modulate the possible transcription of certain mRNA molecules.